Mineral - Willemite
Willemite
Chemical Properties
Mineral Class
Silicates
Toxicity
none
Formula
Zn₂SiO₄
Unit Cell
a=13.95 c=9.32 Z=18
Physical Properties
Hardness
5.5
Streak
white
Density
Heavy (3,5-6)
Cleavage
Indistinct after {11 2 0} and {0001}
Fracture
conchoidal,
uneven
Tenacity
Brittle
Optical Properties
Color
whiteredgreenbluecolorless
Birefringence
0.031
Luster
Vitreous
Transparency
translucent,
transparent
Pleochroism
Geomineralogical Properties
Crystal System
trigonal
Point Group
rhombohedral - 3
Space Group
R 3 (148)
Habit
spherical, prismatic, spherulitic, tabular
Formation
Secondary, formed by metamorphic transformation or hydrothermal metasomatism of zinc deposits (e.g., sphalerite) with the addition of SiO₂ in a silicate-carbonate environment.
Paragenesis
Twinning
Rarity
Rather rare
Synonyms
Willemite
Composition
Elements
Mass
SiO₂
26.55
Al₂O₃
1.00
FeO
0.08
MnO
0.12
ZnO
72.11
MgO
0.13
New Jersey (Dana 1895)
Groups and Members
Phenakite-Group